<template>
  <div class="q-pa-md">
    <q-table
      class="my-sticky-dynamic"
      flat bordered
      title="Treats"
      :rows="rows"
      :columns="columns"
      :loading="loading"
      row-key="index"
      virtual-scroll
      :virtual-scroll-item-size="48"
      :virtual-scroll-sticky-size-start="48"
      :pagination="pagination"
      :rows-per-page-options="[0]"
      @virtual-scroll="onScroll"
    />
  </div>
</template>

<script>
import { ref, computed, nextTick } from 'vue'

const columns = [
  {
    name: 'index',
    label: '#',
    field: 'index'
  },
  {
    name: 'name',
    required: true,
    label: 'Dessert (100g serving)',
    align: 'left',
    field: row => row.name,
    format: val => val,
    sortable: true
  },
  { name: 'calories', align: 'center', label: 'Calories', field: 'calories', sortable: true },
  { name: 'fat', label: 'Fat (g)', field: 'fat', sortable: true },
  { name: 'carbs', label: 'Carbs (g)', field: 'carbs' },
  { name: 'protein', label: 'Protein (g)', field: 'protein' },
  { name: 'sodium', label: 'Sodium (mg)', field: 'sodium' },
  { name: 'calcium', label: 'Calcium (%)', field: 'calcium', sortable: true, sort: (a, b) => parseInt(a, 10) - parseInt(b, 10) },
  { name: 'iron', label: 'Iron (%)', field: 'iron', sortable: true, sort: (a, b) => parseInt(a, 10) - parseInt(b, 10) }
]

const seed = [
  {
    name: 'Frozen Yogurt',
    calories: 159,
    fat: 6.0,
    carbs: 24,
    protein: 4.0,
    sodium: 87,
    calcium: '14%',
    iron: '1%'
  },
  {
    name: 'Ice cream sandwich',
    calories: 237,
    fat: 9.0,
    carbs: 37,
    protein: 4.3,
    sodium: 129,
    calcium: '8%',
    iron: '1%'
  },
  {
    name: 'Eclair',
    calories: 262,
    fat: 16.0,
    carbs: 23,
    protein: 6.0,
    sodium: 337,
    calcium: '6%',
    iron: '7%'
  },
  {
    name: 'Cupcake',
    calories: 305,
    fat: 3.7,
    carbs: 67,
    protein: 4.3,
    sodium: 413,
    calcium: '3%',
    iron: '8%'
  },
  {
    name: 'Gingerbread',
    calories: 356,
    fat: 16.0,
    carbs: 49,
    protein: 3.9,
    sodium: 327,
    calcium: '7%',
    iron: '16%'
  },
  {
    name: 'Jelly bean',
    calories: 375,
    fat: 0.0,
    carbs: 94,
    protein: 0.0,
    sodium: 50,
    calcium: '0%',
    iron: '0%'
  },
  {
    name: 'Lollipop',
    calories: 392,
    fat: 0.2,
    carbs: 98,
    protein: 0,
    sodium: 38,
    calcium: '0%',
    iron: '2%'
  },
  {
    name: 'Honeycomb',
    calories: 408,
    fat: 3.2,
    carbs: 87,
    protein: 6.5,
    sodium: 562,
    calcium: '0%',
    iron: '45%'
  },
  {
    name: 'Donut',
    calories: 452,
    fat: 25.0,
    carbs: 51,
    protein: 4.9,
    sodium: 326,
    calcium: '2%',
    iron: '22%'
  },
  {
    name: 'KitKat',
    calories: 518,
    fat: 26.0,
    carbs: 65,
    protein: 7,
    sodium: 54,
    calcium: '12%',
    iron: '6%'
  }
]

// we generate lots of rows here
let allRows = []
for (let i = 0; i < 1000; i++) {
  allRows = allRows.concat(seed.slice(0).map(r => ({ ...r })))
}
allRows.forEach((row, index) => {
  row.index = index
})

const pageSize = 50
const lastPage = Math.ceil(allRows.length / pageSize)

export default {
  setup () {
    const nextPage = ref(2)
    const loading = ref(false)

    const rows = computed(() => allRows.slice(0, pageSize * (nextPage.value - 1)))

    return {
      columns,
      rows,

      nextPage,
      loading,

      pagination: { rowsPerPage: 0 },

      onScroll ({ to, ref }) {
        const lastIndex = rows.value.length - 1

        if (loading.value !== true && nextPage.value < lastPage && to === lastIndex) {
          loading.value = true

          setTimeout(() => {
            nextPage.value++
            nextTick(() => {
              ref.refresh()
              loading.value = false
            })
          }, 500)
        }
      }
    }
  }
}
</script>

<style lang="sass">
.my-sticky-dynamic
  /* height or max-height is important */
  height: 410px

  .q-table__top,
  .q-table__bottom,
  thead tr:first-child th /* bg color is important for th; just specify one */
    background-color: #00b4ff

  thead tr th
    position: sticky
    z-index: 1
  /* this will be the loading indicator */
  thead tr:last-child th
    /* height of all previous header rows */
    top: 48px
  thead tr:first-child th
    top: 0

  /* prevent scrolling behind sticky top row on focus */
  tbody
    /* height of all previous header rows */
    scroll-margin-top: 48px
</style>
